1. Field
Example embodiments relate to a semiconductor memory device and a system including the same.
2. Description of Related Art
With the development of technology, semiconductor memory devices are continuously becoming more highly integrated and operated at higher speed, and are used in various products ranging from large home appliances to small mobile products. Such semiconductor memory devices each have a plurality of cells for storing data.
Cells may store data in the form of charge, the stored data being determined as “0” or “1” according to a charged amount of charge. Data stored in a cell may be discharged by leakage current and may be lost after a predetermined time. To prevent such data loss, a refresh operation, of storing data of a cell again, may be performed. Where electrical characteristics of cells are different from each other, the cells may have different discharge times. In other words, data retention times of the cells, i.e., times for which the accuracy of data can be ensured, differ from each other. To ensure the reliability of data stored in cells, the refresh operation should be performed before a data retention time passes.